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An article by Wohlers, et al. published yesterday on-line in the Proceedings of the National Academy of Sciences (PNAS) indicates that increasing ocean temperatures associated with global warming reduce the ocean's capacity to serve as a carbon sink. This establishes one of the positive feedback mechanisms that will accelerate global warming over time.Full text PDF: requires subscription The abstract:

The
pelagic ocean harbors one of the largest ecosystems on Earth. It is
responsible for approximately half of global primary production,
sustains worldwide fisheries, and plays an important role in the global
carbon cycle. Ocean warming caused by anthropogenic climate change is
already starting to impact the marine biota, with possible consequences
for ocean productivity and ecosystem services. Because temperature
sensitivities of marine autotrophic and heterotrophic processes differ
greatly, ocean warming is expected to cause major shifts in the flow of
carbon and energy through the pelagic system. Attempts to integrate
such biological responses into marine ecosystem and biogeochemical
models suffer from a lack of empirical data. Here, we show, using an
indoor-mesocosm approach, that rising temperature accelerates
respiratory consumption of organic carbon relative to autotrophic
production in a natural plankton community. Increasing temperature by
2–6 °C hence decreased the biological drawdown of dissolved inorganic
carbon in the surface layer by up to 31%. Moreover, warming shifted the
partitioning between particulate and dissolved organic carbon toward an
enhanced accumulation of dissolved compounds. In line with these
findings, the loss of organic carbon through sinking was significantly
reduced at elevated temperatures. The observed changes in biogenic
carbon flow have the potential to reduce the transfer of primary
produced organic matter to higher trophic levels, weaken the ocean's
biological carbon pump, and hence provide a positive feedback to rising
atmospheric CO2.